QuickSearch Keeps Moving

Hey everyone, I am moving the search bar to the header and am doing so by adjusting the top value only. This is where my problems start, I have edit it in Firebug and check its aligned correctly etc and then I add its value to my extra.css with !important. For some reason after saving its perfectly fine but after a few hours it seems to jump to another position, any ideas what could cause this? Its so weird.

Thank you

I have just checked in Chrome and its aligned correctly, in Firefox it is out of place, heres my CSS for it: